Conventional banknote validators such as the Armatic type AL07 comprise a straight slot through which bank notes are fed and a transport mechanism in the form of a plurality of parallel rollers. In order for the authenticity and value of a banknote to be determined, such apparatus includes optical sensing means. In the aforementioned known validator, the optical sensing means comprises two linear arrays of optical transmitters and receivers arranged across the width of the transport mechanism and two sheet-like light guides having a J-shaped cross-section which direct light from the optical transmitters on to either side of a bank note to be validated and the reflected light back to the optical receivers.
Such validators suffer from a number of disadvantages. Firstly, a banknote being fed into the validator is prone to become crumpled during the operation. Secondly, the use of a large number of optical transmitters complicates the manufacture of the apparatus and necessitates regular balancing of the light levels emitted by the optical transmitters. A further disadvantage arises from the use of a flat transport mechanism since in order to accommodate a full range of bank notes the validator must be significantly wider than conventional coin validators which makes them unsuitable for use in most common vending machines. Yet another disadvantage is the need for a complex power supply for supplying the processor employed in the apparatus to determine the authenticity and value of banknotes to be validated. The present invention aims to overcome the aforementioned disadvantages.
A banknote validator is known from European Patent No. 72237, which includes an optical sensing means for sensing characteristics of a sheet, and guide means for guiding the sheet past the optical sensing means. An elongate optical sensing area extends transversely of the sheet path and light reflected from the surface of a banknote is guided to a single sensing station via a fishtail optical fibre array.